Stabilization of acidic aqueous coating compositions containing an organic coating-forming material

ABSTRACT

An acidic aqueous coating composition containing an organic coating-forming material forms on a metallic surface immersed therein a coating, the weight or thickness of which is related to the time the surface is immersed in the composition. The coating composition, which tends to become unstable as a result of the build up of metal ions in the composition, is stabilized by removing the metal ions with an ion exchange material. Also, in maintaining stability, anionic and/or nonionic surfactants or dispersing agents, which are present in the composition to disperse the organic-coating forming material, are added to the composition in an amount in excess of that which is added to replenish the organic coating-forming material as it is consumed during use. Also, coating compositions treated with the ion exchange material tend to produce coatings which have a textured or grainy appearance. The texturing of coatings can be avoided by contacting the coating composition with the ion exchange material in the presence of a cationic surfactant or an amphoteric surfactant which has cationic properties in the acidic aqueous coating composition, or other material which maintains the relatively small particles of the organic coating-forming material in the composition.

United States Patent 1 1 Hall et al.

[111 3,839,097 1""1451 Oct. 1, i974 1 1 STABILIZATION OF ACIDIC AQUEOUSCOATING COMPOSITIONS CONTAINING AN ORGANIC COATING-FORMING MATERIAL [75]Inventors: Wilbur S. Hall, Plymouth Meeting;

Harry M. Leister, Ambler, both of Pa.

[73] Assignee: Amchem Products, Inc., Ambler, Pa.

[22] Filed: Nov. 20, 1972 [21] Appl. No.: 308,176

Related U.S. Application Data [63] Continuation-in-part of Ser. No.257,107, May 26,

1972, abandoned.

[52] U.S. C1 148/62, 117/113, 117/132 C [51] Int. Cl. C23f 7/00, B44d1/098 [58] Field of Search 117/132 C, 113; 148/6153,

[56] References Cited UNITED STATES PATENTS 3,420,715 1/1969 Ayres148/6.16 3,514,343 5/1970 Bauman 148/62 3,585,084 6/1971 Steinbrecher eta1 148/62 3,592,699 7/1971 Steinbrecher et al 148/62 3,647,567 3/1972Schweri 148/6.15 R 3,709,743 1/1973 Dalton ct a1. 148/62 FOREIGN PATENTSOR APPLICATIONS 1,099,461 1/1968 Great Britain 148/62 OTHER PUBLICATIONSEngineers Handbook, Hesler, Recovery and Treatment, 7 pps. (1961).

Primary ExaminerWilliam D. Martin Assistant Examiner-Harry .1. GwinnellAttorney, Agent, or Firm-Synnestvedt & Lechner 5 7] ABSTRACT An acidicaqueous coating composition containing an organic coating-formingmaterial forms on a metallic surface immersed therein a coating, theweight or thickness of which is related to the time the surface isimmersed in the composition. The coating composition, which tends tobecome unstable as a result of the build up of metal ions in thecomposition, is stabilized by removing the metal ions with an ionexchange material. Also, in maintaining stability, anionic and/ornonionic surfactants or dispersing agents, which are present in thecomposition to disperse the organiccoating forming material, are addedto the composition in an amount in excess of that which is added toreplenish the organic coating-forming material as it is consumed duringuse. Also, coating compositions treated with the ion exchange materialtend to produce coatings which have a textured or grainy appearance. Thetexturing of coatings can be avoided by contacting the coatingcomposition with the ion exchange material in the presence of a cationicsurfactant or an amphoteric surfactant which has cationic properties inthe acidic aqueous coating composition, or other material whichmaintains the relatively small particles of the organic coating-formingmaterial in the composition.

45 Claims, N0 Drawings STABILIZATION OF ACIDIC AQUEOUS COATINGCOMPOSITIONS CONTAINING AN ORGANIC COATING-FORMING MATERIALCROSS-REFERENCE TO RELATED APPLICATION This is a continuation-in-part ofUS. applicationSer. No. 257,107, filed May 26, 1972, now abandoned.

FIELD OF THE INVENTION This invention relates to the application ofcoatings to metallic surfaces. More specifically, this invention relatesto a method for maintaining the stability of a coating composition whichis used to coat metallic surfaces by immersing them in the composition.

The coating composition to which this invention relates is an acidicaqueous composition containing an organic coating-forming material whichis capable of forming on a metallic surface immersed therein a coating,the thickness or weight of which is related to the time the surface isimmersed in the composition. The properties of the coating aredetermined chiefly by the type of organic coating-forming material usedin the composition. For example, a composition containing a resin suchas styrene-butadiene copolymer is capable of forming coatings with goodprotective properties as evidenced by their ability to protect the metalsubstrate from corrosion. On the other hand, coatings having goodlubricating propertiescan be formed from a composition which contains anorganic coating-forming lubricant such as, for example, fatty oils,fatty'acids, waxes and mineral oils.

An example of a coating composition of the type to which this inventionrelates and which forms a coating having good corrosion resistance isone which comprises resin solids dispersed in an acidic aqueous solutioncontaining hydrogen peroxide and hydrofluoric acid. Coating compositionsof this type perform substantially differently, and thus, are to bedistinguished from, a conventional latex, that is a dispersion ofinsoluble resin particles in water. Although a conventional latex can'beutilized to form a resinous coating on a metallic surface by immersingthe surface in the latex, the thickness or weight of the resultingcoating is substantially the same regardless of how long the surface isimmersed therein. On the other hand, the acidic aqueous coatingcomposition to which this invention relates deposits coatings on themetallic surface, the thickness or weight of which is governed by thetime the surface is immersed in the composition. The longer the time ofimmersion, the greater the thickness or weight of the coating.

However, a problem that has been encountered in the use of the acidicaqueous coating compositions to which this invention relates is that asthe composition is used to coat quantities of metallic surfaces, thecomposition eventually becomes unstable. A destabilized composition ischaracterized by flocculation, coagulation or gelling of the organiccoating-forming material. After the composition becomes unstable, it canno longer be used effectively to coat metallic surfaces. For allpractical purposes, the composition is rendered inoperative.

Abortive attempts were made to preserve the stability of the bath ofcoating composition by replenishing the ingredients comprising thecomposition as they were depleted during use of the composition.However,

ents alone was not sufficient to maintain the stability of thecomposition. By way of example, it is noted that a replenished coatingcomposition became unstable notwithstanding that the amounts ofingredients in the composition were about the same immediately prior toits becoming unstable as when the composition was being used toeffectively form coatings on metallic surfaces immersed therein.

This invention is directed to maintaining the stability of a bath of anacidic aqueous coating composition containing an organiccoating-formingmaterial of the type which forms on a metallic surface immersed thereina coating, the weight or thickness of which is a function of the timethe surface is immersed in the composition.

BRIEF DESCRIPTION OF THE INVENTION In accordance with this invention ithas been found that the stability of acidic aqueous coating compositionsof the type referred to above can be maintained by treating the coatingcomposition with an ion exchange material which removes from thecomposition metallic ions which otherwise cause the composition tobecome unstable.

By way of brief explanation, it is noted that when a metallic substrateis immersed in the coating composition to which this invention relates,the composition attacks -the metal surface and metal ions are dissolvedtherefrom. The metal ions cause the organic coatingforming material todeposit on the metallic surface by rendering the material unstable inthe region of the metallic surface. As a bath of the coating compositionis used to coat quantities of metallic surfaces, additional amounts ofmetal ions enter the composition and the concentration thereofincreases. Eventually, the concentration of the metal ions increases tothe extent that the coating composition becomes unstable, that is, theorganic coating-forming material tends to flocculate, coagulate or gelthroughout the whole of the coating bath and not just in the region ofthe metallic surface. In essence, the coating composition is renderedinoperative. In accordance with this invention, the coating compositionis treated with an ion exchange material to extract therefrom the metalions which cause the composition to become unstable. Such metal ions arereferred to herein as excess metal ions. It should be understood that asquantities of metal are coated in a bath of the coating composition,additional metal ions, which are dissolved from the metal surface,continue to render the coating-forming material unstable in the regionof the metallic surface, and that treatment of the coating compositionwith an ion exchange material in accordance with this invention does notinterfere with this process by which the coating is formed on themetallic substrate. In effect, the invention provides a method formaintaining the coating-forming material in the composition stableexcept in the region of or adjacent to the metallic surface.

Other aspects of this invention include: the use of particular types ofion exchange materials to provide important operating advantages;treatment of the ion exchange material to remove therefrom extraneousmaterials which tend to contaminate the coating composition;regeneration of the ion exchange material with materials that tie-upmetal ions displaced from the ion exchange material during regenerationthereof; and

contacting said coating composition with a stoichiometric excess of ionexchange material.

For maintaining stability of the coating composition, the presentinvention includes also within its scope the addition to the compositionof dispersing agent or surfactant for the organic coating-formingmaterial to keep the surface tension of the aqueous coating compositionfrom rising to a level at which the composition tends to becomeunstable. The amount of dispersing agent (anionic or nonionic) added isan amount over and above that which might be added to the compositionwhen replenishing the organic coating-forming material as it is consumedduring use. By adding extra dispersing agent for the organiccoating-forming material to the coating composition and subjecting thecomposition to the ion exchange material, as described briefly above,the coating composition can be maintained stable for an indefiniteperiod during use thereof.

In certain applications, it may be found that after the coatingcomposition is treated with an ion exchange material, the compositionwill begin to form coatings that have a grainy or textured surface. Forsome types of articles, this grainy or textured surface may be verydesirable and aesthetically appealing. On the other hand, the appearanceof such a grainy or textured coating surface may be considered to beaesthetically unappealing and/or functionally disadvantageous.

Another aspect of this invention relates to avoiding or reducing thegraininess or texturing of coatings which are produced from a coatingcomposition of the aforementioned type after it is treated with an ionexchange material to remove therefrom metal ions which tend todestabilize the composition.

In accordance with this invention, a preferred method for reducing thedegree of or avoiding such graininess or texturing of coatings is toincorporate into the coating composition before it is treated with theion exchange material a surfactant which exhibits cationic properties inthe acidic aqueous coating composition. A cationic surfactant or anamphoteric surfactant which exhibits cationic properties in the acidiccoating composition can be used. Preferably an amphoteric surfactant isused. Coating compositions containing such a surfactant are capable ofproducing coatings having a reduced degree of texture or of producingsmooth coatings, that is, coatings which are not grainy or textured inappearance, when they are used to coat metallic surfaces after they havebeen treated with an ion exchange material.

It is noted that surfactants having cationic properties are generallyconsidered to be corrosion inhibitors. Surprisingly, it has been foundthat the presence of the aforementioned type of surfactant does notnecessarily inhibit coating formation notwithstanding that the coatingcomposition to which this invention relates functions by dissolvingmetal ions from the metallic surface contacted therewith. Furthermore,it has been found that the presence of said surfactant in the coatingcomposition does not appear to change adversely the other physical orchemical properties of the coatings.

It is believed that as the coating composition is treated with the ionexchange material, the smaller coating-forming particles which comprisethe organic coating-forming material dispersed in the coatingcomposition tend to be lost, for example, by coalescing into largerparticles, or being absorbed by larger particles, or being adsorbed bythe ion exchange material. It is believed that the grainy or texturedcoatings are formed as a result of a reduced in content or absence ofthe aforementioned smaller particles which originally are contained inthe coating composition, along with larger particles, the latter havinga size, for example, of about 0.2 to about 0.5 micron. The smallerparticles can range in size from about 0.01 to about 0.1 micron. Inaccordance with this invention, there is added to the coatingcomposition a material which functions to maintain the smaller particlesof organic coatingforming material in the composition when it is treatedwith an ion exchange material. As mentioned above, surfactants havingcationic properties in the acidic aqueous coating composition can beused to accomplish this, and preferably an amphoteric surfactant havingsuch properties. However, other materials which function to keep thesmaller particles dispersed in the coating composition can be used also.Examples of such materials include protective colloids.

As will be explained more fully below, dispersing agent for the smallerparticles of the coating-forming material can be included in the ionexchange material. When it is contacted with the coating composition,said dispersing agent is effective in maintaining the smaller particlesof organic coating-forming material in the composition.

Another aspect of the invention, discussed in detail below, is the useof a stoichiometric excess of the ion exchange material.

DETAILED DESCRIPTION OF THE INVENTION It should be appreciated from theabove discussion that the coating compositions to which this inventionrelates are those acidic aqueous coating compositions containing anorganic coating-forming material which compositions dissolve metal ionsfrom a metallic surface immersed therein and which form on said surfacea coating, the weight or thickness of which increases during at least aportion of the time that the metallic surface is immersed in thecomposition.

It is believed that the present invention will be used most widely withthe coating compositions of the type described in U.S. Pat. Nos.3,585,084 and 3,592,699 to Hall and Steinbrecher, assigned to the sameassignee as the present invention. Speaking generally, the coatingcompositions disclosed in the aforementioned patents comprise water, anorganic coating-forming material, an oxidizing agent, and hydrogen ionin an amount sufficient to impart to the composition a pH below 7.Examples of organic coating-forming materials, which can be present inthe acidic aqueous composition in dissolved, emulsified or dispersedform, depending on the nature of the material, include ethylene-maleicanhydride copolymer, polyethylene, polyacrylics, styrenebutadienecopolymer, polyacrylic acids and polytetrafluoroethylene. Examples ofoxidizing agents that can be used in the coating composition arehydrogen peroxide, dichromate, perborate, bromate, permanganate,nitrite, nitrate and chlorate. Examples of acids that can be used in thecomposition are sulphuric, hydrochloric, hydrofluoric, nitric,phosphoric, hydrobromic, hydroiodic, acetic, chloracetic,trichloracetic, lactic, tartaric, polyacrylic, fluoboric, fluotitanic,and fluosilicic. It is noted that an acid which contains an anion thatfunctions as an oxidizing agent can be the source of not only thehydrogen ion, but also the oxidizing agent. An example of such an acidis nitric acid.

The amount of coating-forming material utilized in the acidic aqueouscomposition can vary over a wide range. The lower concentration limit isdictated by the amount of coating material needed to provide sufficientmaterial to form a coating. The upper limit is dictated by the amount ofmaterial which can be incorporated in the acidic aqueous composition.The acid ingredient is used in an amount sufficient to impart a pH ofless than 7 to the composition, and preferably a pH of about 1.6 toabout 3.8. The amount of oxidizing agent that should be used is anamount sufficient to provide an oxidizing equivalent of at least about0.01 per liter of the composition. .(The term oxidizing equivalent whenused herein means the number of grams of oxidizing agent used divided bythe equivalent weight of the oxidizing agent. The equivalent weight ofthe oxidizing agent is the gram molecular weight of the agent divided bythe change in valence of all atoms in the molecular which change valence(usually one element).) Amounts of oxidizing agent which provide anoxidizing equivalent somewhat below 0.01 can be used, but preferably theoxidizing equivalent should be at least within the range of about 0.01.It appears that there is no critical upper limit as to the oxidizingequivalents that are used; however, it is preferred that the oxidizingagent be present in an amount such that the upper oxidizing equivalentvalue is about 0.2. However, it should be understood that the oxidizingagent can be used in an amount to provide an oxidizing equivalent muchhigher than 0.2, for example, one or more.

Preferred resinous coating compositions described in the aforementionedpatents comprise:

a. about 5 g/l to about 550 g/l of resin dispersed in the composition,the source of the resin being a latex thereof;

b. about 0.4 g/l to about 5 g/l of fluoride ion;

c. an oxidizing agent selected from the class consisting of H anddichromate, said agent being present in an amount sufficient to providefrom about 0.01 to about 0.2 of oxidizing equivalent per liter ofcomposition; and

d. hydrogen ion in an amount sufficient to impart a pH to thecomposition of about 1.6 to about 3.8.

With respect to the resin component of the above described preferredcomposition, it is present in the composition in the form of dispersedparticles. This aqueous resin dispersion is preferably supplied as alatex.

The concentration of the resin in the composition has an influence onthe weight of coating that will be obtained, other factors heldconstant. Compositions with greater amounts of a particular resin willproduce higher coating weights.

As set forth above, the preferred aqueous acidic coating compositioncontains fluoride ion. The optimum, preferred method of making thecomposition acidic and adding fluoride ion comprises the use ofhydrofluoric acid. This acid permits a simple means for control over pHrequirements of the composition and obviates the need for introducingthe fluoride ion in the form of an alkali metal, ammonium or other salt.While coatings can be obtained by adding the fluoride in salt form, itis preferred to utilize hydrofluoric acid and avoid the use of saltswhich may give rise to undesirable cations in the coating composition orcomplicate pH adjustment. If the fluoride component is added in the formof a salt, the pH of the composition can be adjusted by the use of acidsother than hydrofluoric or in combination with hydrofluoric. Examples ofsuch acids include sulfuric, phosphoric, nitric and hydrochloric.

As noted hereinabove, the preferred pH value of the acidic aqueous resincoating composition is within the range of about 1.6 to about 3.8. Ifthe pH is permitted to fall below about l.6, the coating composition maytend to etch the metal surface. On the other hand, if the pH of thecoating composition exceeds about 3.8, the composition tends to impartvery thin coatings to the metal substrate.

The oxidizing agent used in the preferred coating composition ishydrogen peroxide or dichromate ion (Cr O Hydrogen peroxide is mostpreferred. The hydrogen peroxide can be added conveniently in the formof a 30 percent aqueous solution of hydrogen peroxide. The dichromateconstituent can be added in the form of a variety of water solublehexavalent chromiumcontaining compounds. Examples of such compoundsinclude chromic acid, potassium dichromate. magnesium dichromate,potassium chromate and sodium chromate. Any water soluble hexavalentchromiumcontaining compound, which in an aqueous acidic medium formsdichromate, can be used. Preferred sources of the dichromate ingredientare dichromates, forexample calcium dichromate. Particularly goodresults have been obtained by utilizing an aqueous solution of chromicacid and a calcium salt, for example calcium carbonate. In addition,particularly good results have been obtained by adding to thecomposition an aqueous solution made up from potassium dichromate andcalcium acetate. It is preferred also that the source of dichromate beadded to the latex used in the form of an aqueous solution of thehexavalent chromiumcontaining compound.

The preferred amount of oxidizing agent is an amount sufficient toprovide an oxidizing equivalent of about 0.01 to about 0.2 in one literof the composition. Somewhat lesser amounts of the oxidizing agent whichprovide an oxidizing equivalent outside of the lower value can beutilized also. The upper equivalent value is not critical and can bemuch higher. For example, resinous coatings have been obtained when theamount of hydrogen peroxide used provided an oxidizing equivalent inexcess of one. It has been observed that when dichromate is utilized asthe oxidizing agent in amounts to provide oxidizing equivalents in thehigher range, then higher amounts of fluoride should be used for example3 /2 to 5 g, when the dichromate equivalent is within the range of about0.1 to about 0.2.

As to particularly preferred amounts of the oxidizing agent, thereshould be utilized about 0.3 to about 3.0 g/l of hydrogen peroxide(approximately 0.02 to 0.2 equivalent) and from about 1 g/l to about 2g/l of dichromate (approximately 0.03 to 0.055 equivalent). However,when an aqueous solution made up from chromic acid and calcium carbonateor when an aqueous soluton made up from potassium dichromate and calciumacetate is used, then lower amounts of dichromate can be utilized andthicker coatings can be obtained, for example about 0.735 g/l to about0.95 g/l of dichromate (approximately 0.02 to 0.03 equivalent).

The above described compositions can be utilized to good advantage toproduce quality coatings, the thickness of which can be controlled bythe time a metallic surface is immersed therein. Also, coatings producedfrom such compositions are initially adherent to the metal surface andresist being removed therefrom when the coated surface is rinsed afterit is withdrawn from the composition. Coatings with good corrosionresistance and adhesion properties can be produced.

An additional coating composition that can be used in the practice ofthe present invention comprises an acidic aqueous solution containingthe aforementioned type of organic coating-forming material, ferric ion,and optionally, an oxidizing agent of the aforementioned type. Theferric ion can be incorporated in the composition by adding thereto ironcompounds which will yield or liberate ferric ion in the composition,such as iron compounds which are soluble in the composition. Examples ofsuch materials include ferric fluoride, ferric nitrate, ferric chloride,ferric phosphate and ferric oxide. The composition can be acidified byadding thereto the aforementioned type of acids. The acidic aqueouscomposition preferably has a pH of about 1.6 to about 5.0 and cancomprise about to about 550 g/l of resin, about 0.025 g/l to about 3.5g/l of ferric ion (preferably about 0.3 g/l to about 1.6 g/l), andoptionally about 0.01 to about 0.2 oxidizing equivalent per liter ofoxidizing agent. Preferred compositions of this type include: about 5 toabout 550 g/l of resin solids added in the form of an anionicallystabilized resin dispersion, about l to about 5 g/l of ferric fluoridetrihydrate and an acid in an amount sufficient to impart a pH of aboutl.6 to about 5.0 to the composition. Preferably, hydrofluoric acid isused and in an amount such that the composition contains about 0.4 toabout 5 g/l of fluoride ion. Such coating compositions are also capableof forming on metallic surfaces coatings, the weights or thicknesses ofwhich are increased, the longer the metallic surfaces are immersed inthe composition. After the coated surface is withdrawn from the coatingcomposition it should be exposed to an oxidative environment, such as byallowing the surface to stand in air for a time of about seconds toabout 10 minutes. Thereafter, the coating can be rinsed and driedthereby providing a tightly adherent and uniform coating on the metallicsurface. It is noted that the time of exposure of the coating (after themetallic surface is withdrawn from the coating composition) to theoxidative environment should not be so long as to allow the coating todry before it is rinsed.

Other optional ingredients can be added to the coating compositions. Theaddition of a coalescing agent, for example, ethylene glycol monobutylether, can enhance the corrosion resistant properites of the coatings.Preferred amounts of the coalescing agents are about 5 to about gramsper liter of the composition. As an aid in assuring thorough wetting ofthe metallic surface during treatment, it is sometimes preferable toincorporate into the coating composition a small quantity of a wettingagent, such as up to about 0.15 percent by weight of the totalcomposition, over and above that which may be present in the source ofthe coatingforming material, for example, a latex. Pigments can beincorporated into the composition to give coatings of the desired colorsand to provide decorative or aesthetic effects.

The coating composition for use in the practice of this invention can beutilized to coat a variety of metallic surfaces. Particularly goodresults have been obtained in the coating of ferriferous and zinciferoussurfaces. Examples of other metallic surfaces that can be coated arealuminum, copper. tin, and lead.

Metallic surfaces which have thereon a previously formed coating alsocan be coated by the coating compositions described above. Suchpreviously formed coatings may be of the crystalline or amorphous types.Process and compositions for applying such coatings are well known. Byway of example, such coatings can include those that are generallyreferred to as phosphates, chromates, oxalates, and oxides (anodized orchemically converted) coatings.

There follows a general description of conditions under which a coatingmay be applied in the practice of this invention.

The time of immersion of a metallic surface in the I coating compositionmay vary from as little as 30 seconds to as much as 10 minutes or evenlonger. As pointed out above, the coating weight, for a particularcoating composition and type of metal surface being treated, tends toincrease, up to a maximum, as the time of treatment is increased. Oncethe operating characteristics of a particular coating system have beenascertained, this fact can be exploited to provide a convenient, readilyvariable, control parameter for securing the desired coating weight. Ifa light coating is desired, a short treating time can be employed, andwhen a heavy coating is desired, the treating time can be lengthened.This advantage is unavailable to those using other types of resinouscoating compositions because the coating weights obtained with othertypes of compositions are not, as a practical matter, a function oftime.

With respect to coating bath temperature, this is preferably operatedanywhere from ambient temperature, that is, from about 20C. up to about40C. Higher temperatures can be used, but temperatures which render thecomposition unstable should be avoided. Advantages can be obtained byimmersing the metallic surface in a heated coating composition. With allfactors held constant except the temperature of the coating bath, it hasbeen found that higher weight coatings can be obtained as thetemperature of the composition is raised. The coating weight begins tofall off as the temperature exceeds a certain limit, which limit willvary depending on the type of coating-forming material utilized informulating the coating composition.

It is preferred that relative motion be maintained between the coatingcomposition and the metallic surface immersed therein. This may beaccomplished, for example, by stirring the composition with a mixer orby moving the surface in the composition. By maintaining relative motionbetween the surface and the composition, heavier or thicker coatings canbe obtained.

Coatings can be formed from the composition without utilizingelectricity as is used in the electrocoat or electrodeposit process forpainting metals. The metallic surface may have an electrical charge as aresult of being immersed in the coating composition, but a chargeapplied from an external source is not needed.

It is noted that numerous examples showing the use of coatingcompositions of the type described above to apply resinous coatings tometallic surfaces are set forth in the aforementioned patents.

The organic coating-forming material in the coating compositionsdescribed in detail above is a resinous or polymeric plastic typematerial. However, as disclosed in aforementioned US. Pat. No.3,585,084, the organic coating-forming material can be also anon-resinous material such as a fatty acid, for example, stearic acid.Coating compositions containing fatty acids and other coating-formingmaterials are described in detail in pending US. patent application Ser.No. 152,992, filed June 14, 1971 (now US. Pat. No. 3,776,848) in thenames of Hall and Steinbrecher. The coating compositions described insaid application are particularly useful in applying to metallicsurfaces coatings which have lubricating properties. The organiccoating-forming material used in these coating compositions is anorganic lubricant. Such coating compositions can be treated also inaccordance with this invention to maintain their stability as they areused to coat quantities of metal.

The coating composition described in the aforementioned applicationcomprises an acidic aqueous coating composition containing an organiclubricant and an oxidizing agent. The coating composition can be used toapply lubricating coatings to metallic surfaces which are to besubjected to metal working operations such as forging, extruding,drawing, stamping, molding, etc. The coatings function to avoid or deterthe marring or seizing of the metallic surface; in addition, wear of thedie surface of the metal working apparatus is reduced.

Any organic lubricant which is capable of forming a coating on ametallic surface from the acidic, waterbased composition described abovecan be used. The vast majority of the organic lubricants are insolublein an acidic aqueous medium. However, such insoluble lubricants can beused provided they are capable of being water-solubilized or aredispersible in the water phase of the composition in the form of liquidor solid particles. In accordance with known methods, this can be donewith the aid of surfactants such as emulsifiers, dispersants, wettingagents, etc.

Examples of organic lubricants that can be used are: fatty oils; fattyacids, waxes; and mineral oils. These broad classes of lubricantsinclude materials such as, for example: sulfurized fatty oils and fattyoils from animals, vegetables and fish; waxes of mineral, vegetable,

' animal or synthetic origin; modified minerals such as sulfurizedmineral oil and light solvents and neutral oils. Such materials, whichare well known, can be used alone or in combination as thecoating-forming lubricant in the acidic aqueous coating compositionprovided that they are capable of being uniformly distributed throughoutthe acidic aqueous phase of the composition. Organic lubricants whichcannot be so distributed will tend to separate from the aqueous phase asby precipitating or forming a water immiscible layer.

Distributing the solid or liquid coating-forming lubricant in theaqueous phase of the composition can be carried out according to knowntechniques. For example, a mixture of solid organic lubricant andemulsifiers or dispersants can be melted and the resulting melt can bedispersed by adding thereto, with stirring, water which has been heatedto a temperature above the melting point of the mixture.

By way of a specific example, stearic acid, a preferred coating-forminglubricant and one which is a solid at room temperature, can be dispersedin water according to known methods. For example, a mixture of stearicacid and dispersing agents can be heated to the melting point of thestearic acid, about 70C; water heated to about the same temperature canbe added slowly with good agitation to the molten mixture until theemulsion inverts from water-in-oil to oil-in-water. Thereafter, theremainder of the water can be added more rapidly. Stirring of thedispersion should be continued as the remainder of the water is addedand during cooling also. To this dispersion, there can be added the acidand oxidizing agent. The resultant coating composition can becharacterized as an acidic aqueous solution of an oxidizing agent havingdispersed therein particles of stearic acid. This method is exemplary ofthe way other water insoluble solid organic lubricants can be dispersedin water. Aqueous dispersions can be made from water insoluble orimmiscible liquid organic lubricants by similar procedures carried outat ambient temperature.

The amount of coating-forming lubricant that can be used in thecomposition can vary over a wide range. The lower concentration limit isdictated by the amount of lubricant needed to provide sufficientmaterial to form a coating on the metallic surface. This will varydepending on the specific coating-forming lubricant that is used. Theupper limit is governed by the amount of lubricant that is capable ofbeing incorporated uniformly throughout the acidic aqueous phase of thecomposition at a viscosity suitable for application. This, too, willtend to vary depending on the specific coating-forming lubricant that isused. In general, heavier lubricating coatings will be formed the higherthe concentration of lubricant present in the composition, othervariables held constant. A preferred coating composition for forminglubricant coatings contains about 20 g/l to about 80 g/l of stearicacid.

The acidity of the coating composition containing the lubricant can varyover a wide range also and is influenced by the other ingredientscomprising the composition, particularly the specific lubricant used.Guidelines for determining an operating pH are as follows. The pH shouldnot be so low that the composition etches, but does not coat, themetallic surface. As the pH is increased above the value at which onlyetching of the metallic surface is effected heavier and heavier coatingscan be formed until, for any given composition, a maximum coating weightis obtained; this will generally occur at a pH well below 7. As the pHis increased toward 7, the coating weights begin to decrease andcoatings which appear to be comprised primarily of inorganic materialsare produced. The optimum pH range for any given composition may be bestdetermined from experience. A pH range of about 2 to about 5 isrecommended for the deposition of stearic acid coatmgs.

The preferred aqueous acidic lubricating coating composition of thisinvention contains fluoride ion. The preferred method for making thecomposition acidic and adding fluoride ion comprises the use ofhydrofluoric acid. This acid permits a simple means for control over pHrequirements of the composition and obviates the need for introducingthe fluoride ion in the form of an alkali metal, ammonium or other salt.While lubricating coatings can be obtained by adding the fluoride insalt form, it is preferred to utilize hydrofluoric acid and avoid theuse of salts which may give rise to undesirable cations in the coatingcomposition or complicate pH adjustment. If the fluoride component isadded in the form of a salt, the pH of the composition can be adjustedby the use of acids other than hydrofluoric or in combination withhydrofluoric. Examples of such acids include sulfuric, phosphoric,nitric and hydrochloric.

With respect to the fluoride ion concentration, amounts within the rangeof about 2 to 8 g/l of compo sition (calculated as F) are preferred.Nevertheless, higher or lower amounts can be utilized. Other variablesheld constant, an insufficient amount of fluoride tends to producecoatings which are thinner than desired; an excess amount of fluoridetends to form coatings which do'not adhere satisfactorily to the metalsubstrate.

The oxidizing agent used in the preferred coating composition is aperoxide. Although metal peroxides such as alkali and alkaline earthmetal peroxides can be used, the use of hydrogen peroxide is mostpreferred. The hydrogen peroxide can be added conveniently to thecomposition in the form of a 30 percent aqueous solution of hydrogenperoxide.

The preferred amount of oxidizing agent is an amount sufficient toprovide an oxidizing equivalent of about 0.1 to about 0.2 in one literof the composition.

Optional ingredients or additives which commonly are used with metalworking lubricants can be added to the composition. Examples of suchmaterials are rust preventatives, odor control agents, antiseptics, etc.

Lubricating coatings formed from the abovedescribed composition haveproperties which prevent metal-to-metal contact thereby facilitatingmetal deformation without galling, scratching, etc. Analyses of thecoatings have shown that they are comprised of both inorganic andorganic components. The inorganic component appears to be comprisedprimarily of metal salts of the base metal. The organic componentcomprises the organic lubricant ingredient of the coating composition.In depositing stearic acid coatings, the organic component can vary overa wide range, for example about 25 wt. to about 95 wt. percent.

Prior to applying the coating composition, the metallic surface shouldbe cleaned.

The contact time between the coating composition and the metallicsurface immersed therein can be controlled as desired. Suitable coatingshaving lubricating properties can be formed usually within about secondsto about 5 minutes. The longer the metallic surface is immersed in thecoating composition the greater the thickness or the weight of thecoating. Analyses of coatings show that the inorganic materials whichmake up the coatings comprise an increasing proportion of the coatingthe longer the metallic substrate has been immersed in the coatingcomposition.

The coating bath is operated preferably at ambient temperature. Elevatedtemperatures can be used, but temperatures which cause the bath tobecome unstable should be avoided. In working with stearic acid baths,it was noted that temperatures in excess of about 100F tended to producecoatings with poor adhesion.

It is preferred that relative motion be maintained between the coatingcomposition and the metallic surface immersed therein. This facilitatescoating formation and improves coating continuity and adhesion.

As mentioned hereinabove, continued use of the coating compositions towhich this invention relates can lead to their becoming unstable as aresult of the buildup of excess metallic ions. By way of explanation, itis noted that the metal ions which are dissolved from the metal surfaceby the coating composition cause, directly or indirectly, theorganic-coating forming material of the composition at the face of themetallic surface to become unstable and deposit on the surface to formthe coating. The exact mechanism by which the metal ions function torender the organic-coating forming material unstable in the region ofthe metal surface can vary depending on the type of organiccoatingforming material used and the type of metal being coated.

For illustrative purposes, certain aspects of the present invention aredescribed in connection with a process utilizing the following coatingcomposition:

COMPOSlTlON A Ingredients Amount. g/l

A) latex comprising 56 wt. 7: about to about 300 of a copolymer ofstyrene butadiene resin solids dispersed in water B) hydrofluoric acidabout [.0 to about 5.0

C) hydrogen peroxide about L5 to about 6.0

D) phosphoric acid about L5 to about 2.5

E) water to make 1 liter The above type coating composition, whichshould have a pH of about 1.6 to about 3.0, has been used to form veryattractive coatings on iron or steel surfaces; the coatings haveexcellent corrosion resistant properties and adhere very tightly to theiron substrate. The phosphoric acid improves the corrosion resistantproperties of the coatings. The resinous coating-forming ingredient, astyrene-butadiene copolymer, is dispersed uniformly in the aqueous phaseof the composition by nonionic surfactants associated therewith. Wheniron is immersed in the composition, the surface thereof is dissolved bythe composition to form ferrous ions which are oxidized by the oxidizingagent, H 0 The ferric ions render the dispersed resin particles unstableat the interface of the iron surface. It is believed that they renderthe dispersing agent ineffective for maintaining the resin particles intheir dispersed state. The destabilized resin particles deposit on theiron surface to form thereon a coating. However, as additional iron orsteel surfaces are immersed in the composition, the amount of ferricions in the composition builds up with the result that the dispersedresin becomes unstable, not only in the region of the metallic surface,but also in other portions of the coating composition. As this occurs,the dispersed resin tends to coagulate, flocculate or gel and thecoating bath can become useless.

The mechanism by which other types of coating compositions used to coatiron or other types of metallic surfaces function may differ to someextent from the mechanism described above. For example, the metal ionswhich are the precursors of coating formation and- /or those which arethe precursors of bath instability may be in a complex form; or they maynot be oxidized from the valence state which they assumed when they weredissolved initially. Also, the metal ions may act directly on theorganic coating-forming material in rendering it unstable. Whatever theexact mechanism, suffree it to say that continued operation of a bath ofthe coating composition of the type to which this invention relates canbe prolonged or operated indefinitely by treating the composition withan ion exchange material which will remove the metal ions which cause,in one way or another, a bath of the composition to become unstable.

The ion exchange material used in treating the coating compositionshould be one which removes the metal ions which build up in thecomposition and cause it to become unstable. The identity of the metalions can be determined by analyzing the composition. The ion exchangematerial, which should be effective in acidic mediums comprising thecomposition, and preferably one which is particularly effective in thepH range of the composition, should be preferably one which extractsselectively the excess metal ions from the coating composition. Speakinggenerally, the ion exchange material can be either a cation exchangematerial or an amphoteric exchange material, the former being muchpreferred. An amphoteric exchanger may remove desirable anions from thebath, as well as the excess metal ions.

The ion exchange material may be a natural occuring material, in itsoriginal or modified form, such as, for example, sulfonated coal andzeolites. It is much preferred to use cation exchange resins becausethey generally have higher exchange capacities. The types of cationexchange resins presently available, and ones popularly used, containfunctional groups such as sulfonic, carboxylic, phenolic, phosphonic andimminodiacetate groups. In treating a coating composition of the A-typeabove which is used to coat iron surfaces, it is preferred to use acation exchange material having a sulfonic functional group because thisgives excellent exchange capacity.

A list of exemplary ion exchange materials which can be used to treatcoating compositions in accordance with this invention is set forthbelow.

Amberlite lR-l 20 (polystyrene nucleated sulfonic acid crosslinked withdivinylbenzene) Amberlite IR-200 (polystyrene sulfonic acid crosslinkedwith divmylbenzene) Amberlyst-l (nucleated polystyrene sulfonic acid)Dowex-SOWXS (polystyrene sulfonic acid crosslinked with divinylbenzene)Ion Exchange Resin C-267 (sulfonated polystyrene, l0% crosslinked withdivinylbenzene) Ion Exchange Resin AGC-243 (sulfonated polystyrene,l2.5% crosslinked with divinylbenzene) For a particular application, thefunctional group and the replaceable cation thereof of the exchangematerial can be selected on the basis of the relative replacing power ofthe cation for exchange with the particular excess metal ion which is tobe extracted from the coating composition. On the basis of availableinformation respecting the exchange properties of the functional groupsand replaceable cations thereof, it may appear advantageous to utilizean ion exchange material that contains replaceable metal ions instead ofreplaceable hydrogen ions. However, for long term use for maintainingthe coating composition stable, it is important that the ion exchangematerial contain replaceable hydrogen ions rather than replaceable metalions. It is noted that the replaceable cation of the ion exchangematerial is released into the coating composition contacted therewith.Thus the use of an ion exchange material which contains replaceablehydrogen ions releases hydrogen ions into the acidic aqueous coatingcomposition. As such, extraneous cations are not introduced into thecomposition. On the other hand, the use of an ion exchange materialwhich contains replaceable metal ions will release such ions, which maybe extraneous material, into the coating composition. Through continuedoperation and treatment of the coating com- I position, such metal ionsmay have an adverse effect on the coating bath and/or on thecoatingsbeing formed. For example, the introduction into the coatingbath of a sufficient amount of extraneous metal ions may cause the bathto become unstable. Also, the corrosion resistance of the coatings maybe reduced by the presence of extraneous metal ions in the bathcomposition.

In treating coating compositions with an ion ex-' change material, itmay be found that the coating composition changes the physical form ofan ion exchange material used. For example, beads of an ion exchangematerial may be fractured upon being contacted with the coatingcomposition; in effect, the beads tend to weaken and crumble. Althoughthis may not affect adversely the exchange capacity of the ion exchangematerial, it may lead to other problems, for example clogging of an ionexchange column charged with the beads. In accordance with thisinvention, it has been found that this problem can be minimized byutilizing a more highly crosslinked ion exchange material.

By way of example, it is noted that when a coating composition of thetype of Composition A above was treated in an ion exchange column ofbeads of an ion exchange material comprising Amberlite lR-120, thecomposition fractured the beads and caused them to crumble. This wasminimized by replacing the aforementioned beads with ion exchange beadscomprising Amberlyst 15, a more highly crosslinked ion exchange resin.

In view of the numerous variables which are inherent in the use of thecoating compositions to which this invention relates, it is impractical,if not impossible, to state a numerical value at which the excess metalions in the coating composition cause it to become unstable.

(Rohm & Haas Co.) (Rohm 8t Haas Co.) (Rohm 8L Haas Co.) (Dow ChemicalCo.) (J. T. Baker Chemical Co.) (J. T. Baker Chemical Co.)

The following factors can have a bearing: the type of metal beingcoated; the specific type of organic coating-forming material comprisingthe composition; the types and amounts of dispersing agents in thecomposition; the rate of throughput of metallic surfaces in thecomposition; the extent to which the composition ionizes metal from themetallic surfaces; and the age of the bath. For this reason, it has beenfound more expedient to make certain empirical determinations respectingthe operatingcharacteristics of specific processes, and then utilizethese determinations as guidelines for adjusting or controlling theamount of excess metal ions which cause the coating compositions tobecome unstable. Information gathered from these empiricaldeterminations can be used to determine the necessary rate of removal ofexcess metal ion from the composition, and the upper limit of metal ionconcentration. This data can be used, in turn, to determine how much ionexchange material should be used as will be explained in detail below.

In general, it will be most convenient to make the empiricaldeterminations on a test bath and then utilize information gathered fromthe determinations in operating a production bath. Periodic analysis ofthe metal content of an operating bath is the preferred way fordetermining when excess metal ions should be removed and the amountthereof that should be removed. It has been found, for any given coatingoperation, the composition will become unstable when the metal ionsbuild up to a certain value. By operating a given coating composition toa state of instability and recording the metal ion content, theconcentration at which any given composition in a particular operationtends to become unstable under the operating conditions can bedetermined. This information can be used in a future like operation toavoid destabilization of the composition. By recording the metal ionconcentration of the composition as metallic surfaces are processedthrough it, steps, as outlined above can be taken to avoid instability.Excess metal ions can be removed from the bath by use of the ionexchange material thereby reducing the concentration thereof in thecomposition.

By way of example, it is noted that in utilizing a coating compositionof the type of Composition A above to coat iron or steel surfaces, thecomposition tended to become unstable as the ferric ion concentrationexceeded about 1.5 g/l. However, a bath of the composition could beoperated for prolonged periods by replenishing the ingredients as theywere consumed and removing ferric ions periodically as theirconcentration approached about 1.5 g/l by treatment with an ion exchangematerial.

The coating composition can be treated with the ion exchange material inany suitable way. For example, it can be contacted with ion exchangemembranes, ion exchange fabrics, or it can be passed through a column ofion exchange beads.

The coating composition can be contacted with the ion exchange materialon a continuous or periodic basis. In operating on a continuous basis,the metal ion content can be maintained at a constant level which isbelow that at which the metal ion tends to cause destabilization of thecomposition. In operating on a periodical basis, the metal ion contentcan be allowed to increase to a predetermined tolerable level beforeremoving it to a desirable level.

The ion exchange material should be regenerated, as needed, in order torestore its ion exchange capacity. Regeneration involves displacing themetal ions adsorbed by the ion exchange material, and replacing themwith cations which will in turn be replaced by the metal ions to beremoved from the composition. For example, in using an ion exchangecolumn packed with beads of the ion exchange material, flow of thecoating composition through the column is terminated. Thereafter, thecolumn is rinsed preferably with water to reclaim residual coatingcomposition in the column. Removal of residual coating composition fromthe column also avoids any tendency for the composition to be coagulatedby the material used to regenerate the ion exchange beads comprising thecolumn. The column can be rinsed conveniently by running watertherethrough. It is preferred to use deionized water. Hard water has atendency to decrease the capacity of the ion exchange material for themetal ions which are to be removed.

The type of regenerating material (often referred to as eluant) usedwill depend on the nature of the ion exchange material. When utilizingan ion exchange material that includes a replaceable hydrogen ion,regeneration can be effected by contacting the material with an aqueoussolution of a strong acid. For example, an aqueous solution ofsulphuric, hydrochloric, phosphoric, or nitric acid can be passedthrough an ion exchange column to regenerate the beads therein. Inregenerating an ion exchange material which has a replaceable cation,other than hydrogen, a concentrated aqueous solution of a saltcontaining the cation can be used. For example, if the ion exchangematerial contains sodium cation, an aqueous solution of brine can beused as the regenerating material or eluant.

It is noted that the ion exchange material will gener ally be selectedfor use on the basis of its affinity for the metal ion to be extractedfrom the coating composition. Thus, high concentrations of theregenerating material should be passed through the column to removetherefrom the metal ions.

The efficiency of regeneration of the ion exchange material can beincreased by adding to the regenerating material a sequestering agentfor sequestering the metal ion which is displaced from the ion exchangematerial. This ties up the metal ion and prevents it from beingreadsorbed by the ion exchange material. In displacing iron ions fromthe ion exchange material particularly good results have been obtainedby utilizing oxalic acid as a sequestering agent. Examples of othersequestering agents that can be used include citric acid and glycolicacid. The sequestering agent should be used in an amount such that itincreases the efficiency of metal ion removal from the ion exchangeresin without greatly increasing the cost of regeneration. For example,the regenerating material can comprise 10 gallons of l020 percent H 50and -200 g of oxalic acid per cubic foot of ion exchange resin.

After the ion exchange material has been treated with the regeneratingmaterial, residual extraneous materials that emanate from the use of theregenerating material should beremoved from the ion exchange material.This can be accomplished by rinsing the ion exchange material withwater, preferably deionized water. To illustrate the importance of thisstep, it is noted that regeneration of the ion exchange material mayleave deposited thereon extraneous anions which are capable of beingpicked up by the coating composition that is subsequently contactedtherewith. The presence of such anions in the coating composition mayaffect adversely desired coating properties, such as wet adhesion.

In some applications wherein the ion exchange material has beenregenerated with an eluant that contains no extraneous ions, the amountof rinsing of the regenerated ion exchange material can be reduced. Forexample, and as mentioned above, phosphoric acid can be included in thecoating composition to enhance the corrosion resistant properties of thecoating. Also, phosphoric acid can be used as a regenerating material.Its use will not leave extraneous ions on the ion exchange materialwhich need necessarily be thoroughly removed therefrom.

With respect to the amount of ion exchange material to be used, it isnoted that the ion exchange capacity of available ion exchange materialsis usually reported in the literature; if not, the ion exchange capacitycan be determined readily. It has been observed that the coatingcompositions of the type to which this invention relates usuallydissolve, in any given operation, about the same amount of metal ionfrom the metallic surfaces treated therein. Thus, knowing the amount orsquare feet of metallic surfaces that are to be treated in the coatingcomposition, the amount of metal ion that is likely to build up in abath of the coating composition can be calculated from empiricaldeterminations. Similarly, the amount of metallic ion in the compositionthat is likely to cause the bath to become unstable can be calculatedalso from empirical determinations of the type described hereinabove.This information, coupled with knowledge of the ion exchange capacity ofthe ion exchange material, can be used to determine the amount of ionexchange material that is needed to extract a given amount of metallicion in a given operation. Stoichiometric amounts of the ion exchangematerial can be used to extract a predetermined amount of metallic ion.

However, it has been found that the peculiar nature of the coatingcomposition to which this invention relates makes it very advantageousto use excess amounts of the ion exchange material. This provides formore efficient operation in maintaining the stability of the coatingcomposition over more prolonged periods of time. By way of example, itis noted that resin beads of an ion exchange material sold as Amberlystl and comprising polystyrene sulfonic acid is reported to have an ionexchange capacity of about 1.5 to about 2.0 pounds of iron per cubicfoot of beads. However, in treating a coating composition of the A-typeabove that was used to coat iron surfaces with the aforementioned ionexchange beads, it was found that the beads were effective in removingonly about 1 pound of iron per cubic foot of beads. Accordingly, morethan 2 cubic feet of beads were used because in this particularoperation it was desired to remove more than 1 pound of iron from thecoating composition.

The extent to which additional amounts of ion exchange material are usedto provide the desired ion exchange capacity for a particularapplication is best determined from experience in view of the numerousvariables inherent in the process. However, for guideline purposes, itis recommended that there be used an amount of ion exchange materialsufficient to provide an ion exchange capacity at least percent abovethe expected or reported capacity.

The removal of metal ions from the coating composition by the use of anion exchange mamterial, as described above, is effective in prolongingthe stability of the coating composition. However, it has been foundthat a coating composition may destabilize as it is used to coatmetallic objects, notwithstanding the removal therefrom of metal ions.In essence, removal of the metal ions by the use of the ion exchangematerial is effective in prolonging stability of the composition, butfor applications in which it is desired that the composition be used formore prolonged periods of time (even indefinite periods of time), othersteps must be taken to maintain the coating composition in a stablestate. It has been found that to achieve more prolonged stability of acoating composition, steps must be taken to control the surface tensionof the composition within certain operating ranges. This can beaccomplished by adding to the coating composition a dispersing agent orsurfactant for maintaining the dispersed coatingforming particles intheir dispersed state. As will be explained in detail below, the amountof dispersing agent added to the composition is an amount over and abovethat which is normally incorporated in the aqueous dispersion ofcoating-forming particles.

By way of explanation, it is noted that as the coating composition isused, the surface tension thereof begins to rise and continues to rise,eventually to a value at which the coating-forming materials flocculate,gel, or coagulate throughout the composition thereby rendering itinoperative. Removal of metal ions from the composition by the use of anion exchange material, as described above, may lower the surface tensionof the composition somewhat and will prolong the stability of thecomposition. However, it has been found that even though theconcentration of the metal ions is maintained at a tolerable level, thatis, at a level at which the stability of the composition is prolonged,continued use of the composition can result in a destabilization thereofif steps are not taken to lower the surface tension by adding to thecomposition additional surfactant or dispersing agent.

By way of example, it is noted that the latex used in preparing acomposition of the type of composition A above, had a surface tension ofabout 33 dynes/centimenter. (Other latices, which are commerciallyavailable, generally have a surface tension within the range of about 30to about dynes/centimeter.) The addition of acid and other ingredientsto such latices does not affect the surface tension thereof to anysignificant degree so that coating compositions prepared from suchlatices can have a like surface tension. (The surface tension of purewater is about 72 dynes/centimeter.) In coating steel panels with theaforementioned type of composition, it has been found that thecomposition tends to become unstable as the surface tension rises toabout 40 to about 50 dynes/centimeter, notwithstanding that thestability of the composition was prolonged initially by maintaining themetal ion concentration of the composition at a tolerable level, forexample, below about 1.5 g/l, by treating the composition with an ionexchange material.

Any suitable dispersing agent or surfactant for the dispersedcoating-forming material can be added to the bath of coating compositionto maintain the surface tension thereof at a desirable and stabilizinglevel. In general, the dispersing agent will be of the anionic ornonionic type. Mixtures of such dispersing agents can be used also.Preferably, the dispersing agent should be the one present in theaqueous coating-forming dispersion used in formulating the coatingcomposition. Examples of classes of anionic dispersing agents that canbe used are: sulfuric acid esters; sulfonic acids; and various types ofcarboxylic acids. Examples of classes of nonionic dispersing agents thatcan be used are: ethoxylated alkylphenols; varius types of esters andamides; aliphatic polyethers; alkyl aryl polyethers; and alkyl oralkylaryl thioethers. Specific examples of dispersing agents that can beused include: nonyl phenoxy polyethoxy ethanol; octyl phenoxy polyethoxyethanol; glycerol monolaurate; sodium Z-ethylhexyl sulfate; dioctylester of sodium sulfosuccinic acid; sodium isopropyl naphthalenesulfonate and sodium lauryl sulfate.

As mentioned above, the amount of dispersing agent used for prolongingstability of the bath of the coating composition is an amount over andabove that which is normally present in an aqueous dispersion ofcoatingforming particles. By way of background, it is noted thatparticles of resin in an aqueous resin dispersion or latex aremaintained in their dispersed state by one or more dispersing agentswhich are associated with the particles, as by being absorbed on thesurfaces of the individual particles. Such dispersions are generallymade by emulsion polymerization in which one or more monomers arepolymerized in water in the presence of dispersing agents or emulsifierswhich function to solubilize the monomer, suspend monomer droplets, andsuspend the polymeric particles which are produced by the polymerizablereaction. Another method for preparing resin dispersions is by postemulsification which includes stirring particles of the resin in waterwhich contains a dispersing agent.

The amount of dispersing agent usually present in such dispersions isrelatively small, for example, about 0.2 to about 3 wt. percent. Theexact composition of most commercially available latices is proprietaryinformation. The latices are difficult to analyze because, in additionto the resin solids, they contain usually many other ingredients, suchas preservatives, anti-rust agents, defoamers, pH buffers, protectivecolloids and plasticizers. Thus, the aqueous resin dispersion used inpreparing the coating composition contains dispersant for thecoating-forming resin particles.

It is noted also that as the composition is used to form coatings onmetallic surfaces, the ingredients thereof are depleted. To maintain theingredients in coatingforming amounts, they have to be replenished. Theresinous ingredient of the composition can be replenished convenientlyby adding additional aqueous resin dispersion containing dispersant forthe resin to the composition. Thus, additional dispersing agent for theresin is added to the composition during replenishment. However, it hasbeen found that additional dispersing agent for the coating-formingresin in an amount over and above that present in the resin dispersionfrom which the bath is made up originally or that added to thecomposition during replenishment is needed to prolong the stability ofthe composition.

in view of the numerous variables which are associated with the coatingcomposition and process described herein, it is impractical, if notimpossible, to state the precise surface tension at which the coatingcomposition will destabilize. This determination can be made best byoperating a test bath and then using this information in operating aproduction bath. By recording the surface tension of a test compositionas it operated to a state of instability, the value at which any givencomposition tends to become unstable under typical operating conditionscan be determined. This information can be used in determining theamount of dispersing agent to add to the composition to maintain thesurface tension thereof below the value at which the composition tendsto destabilize.

Generally speaking, the amount of dispersing agent added will depend on:the type of metal being coated; the specific type of resin dispersioncomprising the composition, particularly the dispersing agentsassociated therewith; the rate of throughput of the metallic surfaces inthe composition; the age of the composition; the metallic ion content ofthe composition; and the specific dispersing agent added to thecomposition. In view of the numerous variables that are inherent in thecoating process, it is difficult, if not impossible, to specify theamount of dispersing agent which should be added to the composition toprolong stability. This is best determined from experience in theoperation of a specific coating process. However, for guidelinepurposes, it is noted that the addition to the coating composition ofabout 0.1 to about 5 g/l of nonionic and/or anionic dispersing agent canbe effective in prolonging stability of the composition. A good generalrule to follow is to add the dispersing agent to the composition in anamount which will restore the surface tension thereof to its originalvalue. If too large an amount of dispersing agent is added, the coatingsformed by the composition will tend to be thinner. more water sensitiveand exhibit lower corrosion resistance. It should be understood that theabove amounts are given for guideline purposes and that smaller orhigher amounts may be used satisfactorily in a particular coatingoperation.

By way of example, it is noted that a particular coating compositionfalling within the description of Composition A above had a surfacetension of 39.8 dynes/cm. After processing 4 square feet of steel/literof the composition, the surface tension thereof rose to 44.4 dynes/cm.Addition of 0.5 g/l of a surface active agent (Triton N- nonyl phenoxypolyethoxy ethanol) to the composition lowered the surface tensionthereof to 37.0 dynes/centimeter. Past experience had demonstrated thatif the surface tension of the composition had been allowed to rise muchhigher than 44.4 dynes/centimeter, the composition would havedestabilized. By lowering the surface tension as described,destabilization was avoided. The aforementioned procedure can berepeated indefinitely as the composition is used to coat metallicsurfaces provided that the consumed ingredients thereof are replenishedand excess metal ions are removed from the composition.

Although addition of dispersing agent is effective to prolong stabilityof the composition, this treatment cannot be relied upon exclusively tomaintain the composition in a stable state over a long period of time.As the metal ions continue to build up in concentration, furtheradditions of dispersing agent are not effective in maintaining stabilityindefinitely. Metal ions must be extracted to attain more prolongedstability. For example, in coating steel panels with a composition ofthe Atype above, the ferric ion concentration was allowed to build up inexcess of 1.5 g/l while additional dispersing agent was added to thecomposition. However, upon continued use of the composition, it wasfound that it became unstable when the iron concentration in the bathreached about 3 g/l notwithstanding that additional amounts ofdispersing agent were added to the composition. For more prolonged use,the composition needed to be treated with the ion exchange material tolower the concentration of the ferric ions.

EXAMPLES EXAMPLE 1 Four liters of a bath of the following acidic aqueouscomposition was prepared:

Ingredients Amounts, g/l

latex containing 56 wt.%

of sytrene-butadiene resin solids dispersed in water by a nonionicdispersing agent (pliolite 49l) 21% aqueous solution of HF 15 35%aqueous solution of H 0 8 -Continued Ingredients Amounts, g/l

black pigment dispersion l (Aquabluk 100) water to make 1 liter Fourliters of the above composition were used to coat 16 sq. ft. of steelpanels. The composition was then analyzed and found to contain 1.58 g/lof iron. Previous experience with this type of coating operationindicated that the composition was likely to become unstable if the ironconcentration was allowed to increase to higher amounts. To avoiddestabilization, the composition was passed through an ion exchangecolumn containing about 0.02 cubic feet of ion exchange resin beadscomprising polystyrene nucleated sulfonic acid crosslinked withdivinylbenzene (Amberlite IR-l). After the coating composition was thustreated, it was found to have an iron concentration of 0.025 g/l. Thecomposition was used to coat additional steel panels and remainedstable. The aforementioned process was repeated six times at intervalswhen the iron concentration built up to about 1.0 to about 1.5 g/l. Eachtime the ion exchange beads were regenerated with 2,500 ml of 20 percentH 80 EFCKWLEQ The following acidic aqueous composition was pared:

A 4-liter bath of the above composition was used to coat 4 by 6 inchessteel panels by immersing the panels in the composition for threeminutes one after the other. The panels withdrawn from the compositionwere rinsed, baked and found to have a coating thickness of about 0.8mil. The number of panels coated was such that 120 sq. ft. of steelpanels were coated in the bath of composition. At the start of thecoating operation and thereafter, the composition was analyzed for ironcontent. Previous experience with this type of coating operationindicated that the composition would tend to destabilize when the ironconcentration in the composition built up in excess of about 1 1.5 g/l.In order to avoid destabilization due to excess iron content, thecoating composition was passed through an ion exchange column containing150 ml of cation exchange resin beads (Amberlyst 15) when the ironconcentration reached about 0.5 1 g/l. As additional panels wereprocessed in the composition, and as the composition was passedcontinuously through the ion exchange column, the composition and theeffluent from the column were analyzed for iron content. Whenever 22 theiron concentration in the effluent from the ion exchange column wasabout the same as that in the composition, the coating operation wasstopped, the resin 0 the ion exchange column, the iron concentration inthe composition was maintained at about 0.5 1 g/l. In addition toremoving iron from the composition in the aforementioned manner, theingredients of the composition that were consumed during use werereplenished; also, in order to maintain stability, a nonionic surfaceactive agent was added to the composition. (The surface tension of theoriginally prepared composition was about 38 dynes/cm; experience withthis type of coating operation indicated that the composition woulddestabilize if the surface tension was allowed to rise to about 45-50dynes/cm.) Replenishment of ingredients and addition of the surfaceactive agent were made by continuously adding to the composition theingredients set forth below, the amounts of ingredients given belowbeing the total amounts of ingredients that were added to thecomposition during the entire coating operation.

ingredients ethanol (Triton N nonionic surface active agent) Bycontinuously replenishing the composition and adding thereto thenonionic surfactant, the amounts of ingredients in the composition weremaintained at a substantially constant level and the surface tensionthereof was maintained below about 40 dynes/cm.

By following the above procedure, the coating composition was preventedfrom destabilizing. Calculations showed that during the coatingoperation, a total of about 42 g of iron was dissolved from the panelstreated in the bath. At the end of of the coating operation, analysis ofthe coating composition showed that the iron content thereof was about0.869 g/l. The ion exchange column was effective in removing a total ofabout 38.52 g of iron from the composition during the coating operation.

It is noted that the process described in Example 2 above can becharacterized as a semi-continuous process in that the coating operationwas terminated in order to regenerate the ion exchange column.Termination of the coating process could be avoided and the process madecontinuous by utilizing two ion exchange columns, one of which can beused to remove metal ions from the coating composition while the otheris being regenerated.

CONTINUATION OE DETAILED DESCRIPTION OF THE INVENTION As mentionedabove, it has been observed that coating compositions of the type towhich this invention relates can function to form on metallic substratessmooth and/or glossy coatings before they are treated with the ionexchange material as described above. However, after treatment with theion exchange material, the coating composition can tend to form on themetallic surfaces coatings which are grainy or textured in appearance.If this type of coating is not desired, the use of a dispersing agentfor maintaining the smaller particles of organic coating-formingmaterial in the coating composition should be employed in accordancewith this invention. Excellent results have been obtained by using asurfactant having cationic properties in the acidic aqueous composition.

Surprisingly, nonionic and anionic surfactants are not effective inavoiding or minimizing the textured appearance of coatings formed from acoating composition that has been subjected to the ion exchangematerial.

In accordance with this invention, a cationic surfactant or anamphoteric surfactant which in the acidic medium of the coatingcomposition has cationic properties, can be used to minimize or avoidthe formation of textured coatings. Mixtures of these surfactants can beused also. In addition, a protective colloid, alone or in combinationwith the aforementioned surfactants, can be used.

Any cationic surfactant can be used. Many of the presently availablecationic surfactants are simple amine salts, quaternary ammonium saltsor amino amides and amidazolines. Examples of cationic surfactantsinclude: aliphatic primary amine acetates having the formula RNH COOCHwherein R is an aliphatic hydrocarbon group having about 8 to about 18carbon atoms, for example, undecylamine acetate, heptadecylamine acetateand octadecylamine acetate; polycondensation products obtained byreacting dicyanodiamides, dicyanodiamidine, guanidines, or diguanidineswith formaldehyde; picolinium salts, for example, lauryl picoliniumbromide; polyoxethylene alkyl amines, for example, tetradecaoxyethylenepentadecylamine and dioctaoxyethylene heptadecylamine; pyridinium salts,for example, cetylpyridinium bromide and lauramidomethyl pyridiniumchloride; quaternary ammonium salts, for example, trimethyloctadecylammonium chloride; trimethylcetyl ammonium bromide, anddimethylcetylbenzyl ammonium chloride. Other cationic surfactants can beused and mixtures thereof can be used. Many of the presently availableamphoteric surfactants contain amino and carboxyl groups or amino andsulfuric ester or sulfonic groups. Examples of amphoteric surfactantsthat can be used are: N-coco beta-amino propionic acid; N-lauryl,myristyl betaamino propionic acid; and compounds of the formula:

H CHzC O ONa (Formula I) and Ol-I CH2C O ONa (Formula. II)

Amphoteric surfactants are sold by the Miranol C hemical Co., Inc. underthe trademarks Miranol L2M-SF (Formula I above) and Miranol C2M-AA(Formula II above) and by General Mills, Inc. under the trademarksDeriphat 15 1C (N-coco beta-amino propionic acid) and Deriphat C(N-lauryl, myristyl beta-amino propionic acid).

Other dispersing agents that can be used to minimize or avoid theformation of textured coatings include protective colloids. Theprotective colloid selected for use should be a stable material, thatis, a material which is not degraded by the acidic coating composition.Examples of protective colloids that can be used are water solublecellulose such as hydroxyethyl cellulose, methyl cellulose,carboxymethyl cellulose and synthetic resinous materials, such aspolyoxyethylene, polyacrylic acid and polymethacrylic acid.

In the practice of this invention, it is preferred to use surfactantshaving cationic properties. The use of protective colloids, particularlyhydrophilic protective colloids, can result in a reduction in thecorrosion resistance of the coatings; this has not been observed in theuse of surfactants having cationic properties.

The dispersing agent must be present when the coating composition iscontacted with the ion exchange material. This can be effectedconveniently by incorporating the dispersing agent into the coatingcomposition before it is treated with the ion exchange material. Othermethods for effecting this can be used also. For example, the dispersingagent or an aqueous solution thereof can be added to a column of ionexchange resin beads; also, an ion exchange membrane or fabric can beimpregnated or saturated with the dispersing agent.

The dispersing agent should be used in an amount at least sufficient toreduce the texture of the coatings to the desired degree. This will beinfluenced by a number of factors, for example: the specific dispersingagent used; the specific type of coating composition, and particularlythe specific type and amount of organic coating-forming material used,and the particle size and particle size distribution thereof. In view ofthe number of different variables that are inherent in the use of thisinvention, it is recommended that for any particular coating operation,the amount of the dispersing agent used be determined from empiricalobservations, that is, by using different amounts of the dispersingagent until an amount which gives coatings of the desired smoothness hasbeen employed. It appears that there is no upper limit on the amount ofdispersant that can be used with respect to its functioning to reducetexturing.

There are guidelines which can be used in determining the maximum andminimum amounts of dispersing agent used. For example, the use ofrelatively high amounts of the dispersing agent can reduce the corrosionresistance of the coatings. This may be disadvantageous if coatings withsuch properties are desired. Also, it has been found that the rate ofcoating formation on the metallic substrate may be reduced by utilizinngrelatively high amounts of the dispersing agent. As will be explained inmore detail below, relatively high amounts of certain types ofdispersing agent may cause a coating composition formulated from certaintypes of latices to destabilize. It has been found that there are rangesof concentrations of the dispersing agent which can be used to reduce oravoid the formation of grainy or textured coatings without causing theaforementioned problems.

For guideline purposes, it is noted that coatings having reduced textureand improved smoothness have been obtained by utilizing at least about0.05 g/l, and preferably at least about 0.1 g/l, of the dispersing agentin the coating composition. Coatings with particularly good smoothnesshave been obtained by utilizing at least about 0.2 g/l of the dispersingagent. Amounts in excess of about 0.5 g/l of the dispersing agent havebeen found to result in coatings having reduced corrosion resistance,and higher amounts can lead to the other problems mentioned above, saidhigher amounts being influenced by the particular combination ofvariables used in a particular process. It should be understood that theeffectiveness of the dispersing agents can vary, for example, some beingmore effective at lower concentrations than others. Thus, experience mayshow the desirability of departing from the aforementioned guidelinesrespecting amounts. The desired results can be achieved readily byadjusting the concentration of the dispersing agent.

As mentioned above, latices contain anionic or nonionic materials whichhave surface active properties for maintaining the resin particlesdispersed therein. Such latices usually contain protective colloidsalso, for example, in amounts of 0.l to 1 wt. percent. The presence inthe latex of such anionic and/or nonionic surfactants is effective inmaintaining the smaller sized resin particles dispersed in thecomposition before it is treated with the ion exchange material, but notafter it is so treated. This requires the use of the dispersing agent ofthis invention, for example, the cationic or amphoteric surfactant orthe protective colloid in amounts over and above that which may bepresent in the latex.

Generally speaking, the size of the resin particles dispersed in a latexranges from about 0.01to about 0.5 micron. It is believed that when thecoating composition containing the latex is contacted with an ionexchange material, the smaller sized particles of dispersed resin, forexample, those of size about 0.01 to about 0.1 micron, coalesce witheach other or with larger particles or they are physically adsorbed tothe ion exchange resin. It is believed also that this leads to theformation of textured coatings when the composition is usedsubsequently. Although it is believed that this explanation respectingthe source of the texturing problem is accurate, the problem may ariseas a result of other phenomenon. Whatever the source of the problem, theuse of the cationic or amphoteric surfactants or the protective colloidalleviates it.

As pointed out above, latices contain anionic or nonionic dispersingagents or mixtures thereof which maintain the resin particles of thelatex dispersed therein. (For convenience, a latex in which the resinparticles are dispersed by an anionic dispersing agent is referred tohereafter as an anionically dispersed latex," and a latex in which theresin particles are dispersed by a nonionic dispersing agent is referredto hereafter as a nonionically dispersed latex") in the development ofthis invention, it has been found that a cationic or amphotericdispersing agentcan be readily and satisfactorily' incorporated in acoating composition containing a nonionically dispersed latex, but thatcertain precautions may have to be taken when these dispersing agentsare incorporated into a coating composition containing an anionicallydispersed latex. Speaking generally, it has been found that there is arisk that the addition of an amphoteric or cationic dispersing agent toan acidic aqueous coating composition containing an anionicallydispersed latex will cause the coating composition to destabilize bygelling, coagulating etc.

It is believed that destabilization occurs as a result of the amphotericor cationic dispersing agent neutralizing the charges of the anionicdispersing agent of the latex, thereby rendering the anionic dispersingagent ineffective for maintaining the resin particles of the coatingcomposition in their dispersed state. If this occurs, certainformulating techniques should be used in combining the amphoteric orcationic dispersing agent with the anionically dispersed latex. Inaccordance with the present invention, the recommended technique is toadd the cationic or amphoteric dispersing agent to the anionicallydispersed latex before the latex is acidified; thereafter, the resultingcomposition can be acidifled by adding acid thereto to produce thedesired acidic aqueous coating composition. in preferred form, theamphoteric or cationic surfactant should be diluted with water first,for example, to a concentration of about 1.0 to about 20 g/l of activedispersing agent to fonn a dilute aqueous solution thereof. The latex isthen added to said dilute aqueous solution of dispersing agent, andthereafter, the oxidizing agent and an appropriate amount of acid toacidify the composition to the desired pH are added. By performing theaforementioned mixing techniques, the amphoteric or cationic dispersingagent can be incorporated into the coating composition withoutdestabilizing it. However, it is noted that with respect to the use ofsome cationic dispersing agents, even performance of the aforementionedmixing techniques may not be effective in producing a stable coatingcomposition which contains an effective amount of cationic dispersingagent for reducing the grainy or textured appearance of a coating to thedesired degree. With respect to such cationic dispersing agents, thepreferred mixing techniques may be effective in incorporating thecationic dispersing agent in the coating composition withoutdestabilizing it, but not in amounts which are sufficient to reduce thetextured and grainy appearance of the coatings to the desired degree.Such cationic dispersing agents are best used in combination with acoating composition formulated from a nonionically dispersed latex.

As the dispersing agent is used in accordance with this invention, theamount thereof will tend to be depleted, for example, by dragout, lossto the ion exchange material, etc. Thus, this ingredient should bereplenished as needed. For example, additional amounts of the dispersingagent can be added to the coating composition or to the ion exchangematerial.

Also, in accordance with this invention, it has been found that the useof the dispersing agent may have an effect on the expected ion exchangecapacity of the ion exchange material, which effect makes itadvantageous to use higher amounts of the ion exchange material, amountshigher than the recommended stoichiometric excess discussed hereinabove.For example, and as mentioned above. the ion exchange capacity of resinbeads sold as Amberlyst I5 is reported to be about 1.5 to about 2.0pounds of iron per cubic foot of beads. However, the use of a surfactanthaving cationic properties in a coating composition of the type to whichthis invention relates reduces the ion exchange capacity of the ionexchange material. For example, when a composition of the A-type above,and one which contained the amphoteric surfactant of Formula I above,was used to coat iron surfaces, treatment thereof with theaforementioned ion exchange beads showed that the ion exchange capacityof the beads was about 0.7 pound of iron per cubic foot of beads.

The extent to which additional amounts of ion exchange material are usedto provide the desired ion exchange capacity for a particularapplication in which there is used a coating composition containing asmall particle size dispersing agent is best determined from experiencein view of the numerous variables inherent in the process. However, forguideline purposes it is recommended that there be used an amount of ionexchange material sufficient to provide an ion exchange capacity of atleast about 65 percent above the expected or reported capacity.

The coating composition for use in this invention can be prepared orreplenished conveniently from an aqueous concentrate comprising:

A. about 50 g/l to about 600 g/l of resin solids dispersed in water; and

B. about 0.2 g/] to about 20 g/l, of the small particle dispersingagent, preferably an amphoteric surfactant having cationic properties inan acidic medium. Other ingredients that can be included in theconcentrate are about 5 g/l to about 40 g/l of a nonionic or anionicsurfactant, and/or about 0.3 g/] to about 400 g/l of pigment. It shouldbe appreciated that some types of pigments can be used in very smallamounts to give the desired color, whereas relatively large amounts ofother types of pigments will need be used to give the desired color.

To the above concentrate, which generally will have a pH of about 5 toabout 1 l, the other ingredients comprising the composition, andadditional water, can be added to givean aqueous acidic coatingcomposition containing, for example, about 5 g/l to about 550 g/l ofresin particles dispersed in the composition; about 0.4 g/l to about 5g/l of fluoride ion; an oxidizing agent selected from the classconsisting of H and dichromate, said agent being present in an amountsufficient to provide from about 0.01 to about 0.2 of oxidizingequivalent per liter of composition; hydrogen ion in an amountsufficient to impart to the composition a pH of about 1.6 to about 3.8;about 0 to about 300-g/l of pigment; and at least about 0.05 g/l andpreferably at least about 0.1 g/l of said dispersing agent, preferablyan amphoteric surfactant.

Smooth glossy black coatings have been very effectively applied to ironsurfaces using the following type of composition: about 40 g/l to about200 g/l of styrene-butadiene copolymer dispersed in the composition;about 1 g/l to about 3 g/l of hydrofluoric acid; about 1 g/l to about 3g/l of hydrogen peroxide; about 0 g/l to about 5 g/l phosphoric acid;about 0.35 g/l to about 3.5 g/l of a black pigment such as Aquablak 100,and about 0.2 g/l to about 0.4 g/l of an amphoteric surfactant such asthose of Formulas l and II above; and wherein said composition has a pHof about 1.6 to about 3. Smooth glossy black coatings having a thicknessof about 0.5 to about 1 mil can be applied to iron or steel articles byimmersing them in the composition for about I to about 5 minutes. Tomaintain the stability of the composition as it is used to coat amultiplicity of articles, it is recommended that it be treated with anion exchange material when the concentration of iron in the compositionbuilds up to about 0.1 g/l to about 1 g/l. Very effective results havebeen attained by passing this type of composition through a column ofion exchange resin comprising beads of a nucleated polystyrene sulfonicacid. After the composition is so treated, it can be used to apply toadditional iron or steel articles coatings which are smooth and glossyblack in color.

ADDITIONAL I EXAMPLES Examples set forth below are illustrative of theuse of this invention in forming coatings which are smooth or which havea reduced grainy or textured appearance. Comparative examples are setforth also.

In Example 3 below, and examples which follow, the coating compositionswhich were treated with the ion exchange material did not have metalions therein because freshly prepared compositions were used in thecoating work. Experience has shown that the composition forms texturedcoatings after treatment with the ion exchange material whether or notmetal ions are present in the composition. The work on which theexamples are based was carried out in this way to avoid the timeconsuming process of coating many square feet of metal; this would berequired to build up the metal ion concentration in the composition, butis not necessary to illustrate the practice of the invention as itrelates to the solution of the texturing problem.

EXAMPLE 3 This example illustrates the formation of textured coatingsfrom a coating composition which has been treated with an ion exchangematerial. The following acidic aqueous coating composition was prepared.

Ingredients Amounts, gll

A) latex comprising 56 wt. 7: of a copolymer of styrene-butadiene resinsolids dispersed in water by a nonionic dispersing agent (Pliolite 491)B) hydrofluoric acid 2.10

C) hydrogen peroxide 2.26

D) carbon black pigment dispersion (Aquablak I00) 5.00

composition and baking at a temperature of 400F for about minutes, therewas obtained a black resinous coating on the panel that was verytextured in appearance. It is noted that when the composition of Example3 is used to coat steel panels without first subjecting the compositionto an ion exchange material, the resultant coatings are smooth, that is,they are not textured.

The next four examples show the separate additions to coatingcompositions of Example 3 above of four different surfactants prior tomixing the coating composition with the aforementioned ion exchangebeads. After adding the surfactants to the coating compositions, theprocedure described in Example 3 was followed. The surfactants used andthe amounts thereof Arquad 2C-75 The coating formed from the compositionof Example 4 was completely free of texturing and those formed from thecompositions of Examples 5 and 6 weresomewhat textured, but the degreethereof was very significantly less than that of the coating formed fromthe composition of Example 3 which contained no surfactant. The coatingformed from the composition of Example 7 contained more texturing thanthe coatings formed from the compositions of Examples 5 and 6, but wasmuch less textured in appearance than the coating formed from thecomposition of Example 3. Comparison of the coating of Example 3 withthose of Examples 4 to 7 showed strikingly how the use of a cationic oramphoteric surfactant can be used to avoid or reduce formation oftextured coatings when such coatings are not desired. It is noted thatthe surfactants used in Example Nos. 4 and 5 were amphoteric surfactantsand that those used in Examples 6 and 7 were cationic surfactants.

Other examples of dispersing agents within the scope of this inventionthat have been used effectively to reduce texturing are polyoxyethylenetallowamine (Ethomeen T/25) and octyl amine (Armeen 2D). On the otherhand, the use of a nonionic or anionic surfactant has been found to beineffective for this purpose.

Examples 8 to 14 below illustrate the effect that an amphotericsurfactant has on the thicknesses of coatings formed from coatingcompositions containing different amounts of the surfactant. Thefollowing acidic aqueous coating composition was prepared:

ingredients Amounts, g/l

A) latex comprising 56 wt. of a 100 copolymer of styrene-butadiene resinsolids dispersed in water by a non- -Continued Ingredients Amounts. g/l

ionic dispersing agent (Pliolitc 49]) B) hydrofluoric acid 2.] C)hydrogen peroxide 2.4 D) phorphoric acid 5.)

Table 2 Example Amphoteric Surfactant Coating Thickness.

No. g/l mil It can be seen from Table 2 above that the thicknesses ofthe coatings on the panels tended to decrease as the concentration ofthe amphoteric surfactant was increased. Thus, to maximize coatingthickness in a particular operation, this surfactant should be used inthe lower amounts. The coated panels of Examples 8 to 14 above weresubjected to a salt spray test for hours (ASTM 3-1 17). It was observedthat the use of the amphoteric surfactant did not affect the corrosionresistance of the coated panels adversely.

The next group of examples shows the use of the same amphotericsurfactant and coating composition used in Examples 9 to 14 above toform coatings on panels after the composition was subjected to a cationexchange resin. After the amphoteric surfactant was added to thecompositions in the amounts indicated in Table 3 below, the compositionswere passed through an ion exchange column charged with resin beadscomprising polystyrene sulfonic acid which was crosslinked withdivinylbenzene (Dowex 50W-X8). Thereafter the compositions were used tocoat steel panels by immersing them in the coating compositions for 3minutes. The appearances of the coated panels are set forth in Table 3.

Table 3 Appearances of Coatings formed from Coating Com- EXAMPLE N0. 18

The same procedure as described in Example No. 2 was followed. Coatingsproduced on the steel panels persing agent is a protective colloid.

before the coating composition was passed through the ion exchangecolumn were smooth. After the composition was passed through the ionexchange column, textured coatings were formed on the panels. To reducethe degree of texturing, there was continuously added to the bath ofcomposition, along with the replenished ingredients and the nonionicsurfactant, an amphoteric surfactant, namely the surfactant of Formula 1above. The total amount of amphoteric surfactant added to thecomposition during the coating operation was 2.28 g. After theamphoteric surfactant was added to the composition and the compositionwas passed through the ion exchange column, it formed smooth coatings onthe panels immersed therein.

In summary, it can be stated that the aforementioned We claim: 1. In theprocess for applying an organic coating to objects having a metallicsurface by immersing said object in an acidic aqueous coatingcomposition containing dispersed solid particles of an organiccoating-forming material for a period of time sufficient to form on saidmetallic surface an organic coating, the thickness or amount of whichincreases during at least a portion of the time said surface is immersedin said composition, wherein said composition dissolves from saidsurface metal ions which tend to cause said composition to becomeunstable; and wherein said particles have a size within the range ofabout 0.01 to about 0.1 micron and larger; and wherein said compositionis contacted with an ion exchange material which removes said metal ionsfrom said coating composition thereby maintaining said compositionstable; and wherein said coating composition prior to being contactedwith said ion exchange material forms on said surface a smooth or glossycoating; and wherein said composition after being treated with said ionexchange material tends to form on said surface a coating which isgrainy or textured in appearance; the improvement comprising contactingsaid composition with said ion exchange material in the presence of adispersing agent which is effective in maintaining dispersed in saidcomposition said particles having a size within the range of about 0.01to about 0.1 micron, and thereafter coating said metallic surface withthe thus treated composition containing said particles having a sizewithin the range of about 0.01 to about 0.1 micron thereby forming onsaid metallic surface a smooth coating or a coating which has a reducedgrainy or textured appearance.

2. A process according to claim 1 wherein said particles are resinparticles.

3. A process according to claim 2 wherein said dis- 4. A processaccording to claim 2 wherein said coating composition includes a blackpigment.

5. A process according to claim 2 wherein said dispersing agent is asurfactant having cationic properties in said acidic aqueouscomposition.

6. A process according to claim 5 wherein said surfactant is anamphoteric surfactant.

7. A process according to claim 6 wherein the amount of said amphotericsurfactant in said composition is at least about 0.05 g/l.

8. A process according to claim 7 wherein the amount of said amphotericsurfactant in said composition is about 0.1 to about 0.5 g/l.

9. A process according to claim 5 wherein said composition is contactedwith an amount of ion exchange material that is at least about 65percent above the amount theoretically needed to remove a predeterminedamount of said metal ions.

10. A process according to claim 9 wherein said metal ions are iron ionsand wherein said surfactant is an amphoteric surfactant.

11. A process according to claim 10 wherein said ion exchange materialis a nucleated polystyrene sulfonic acid.

12. A process for applying a coating to objects having a metallicsurface comprising:

A. immersing said object in an acidic aqueous coating composition whichcomprises:

a. about 5 g/l to about 550 g/l of resin dispersed in the composition,the source of the resin being a latex thereof;

b. about 0.4 g/l to about 5 g/l of fluoride ion;

c. an oxidizing agent selected from the class consisting of H 0 anddichromate, said agent being present in an amount sufficient to providefrom about 0.01 to about 0.2 of oxidizing equivalent per liter ofcomposition; and

d. hydrogen ion in an amount sufficient to impart a pH tothe compositionof about 1.6 to about 3.8 wherein said composition dissolves from saidsurface metal ions which tend to cause said composition to becomeunstable;

B. contacting said composition with an ion exchange material whichremoves metal ions from said coating compositions thereby maintainingsaid composition stable, wherein said composition after being contactedwith said ion exchange material tends to form on said metallic surface acoating which is grainy or textured in appearance; and

C. contacting said composition with said ion exchange material in thepresence of an amphoteric or cationic surfactant in an amount sufficientto form on said surface a smooth coating or a coating which has areduced grainy or textured appearance.

13. A process according to claim 12 wherein said metallic surface is aferriferous surface, wherein said metal ions are iron ions and whereinthe concentration of of iron ions in the composition is maintained belowabout 3 g/l.

14. A process according to claim 13 wherein iron ions are removed fromthe composition to keep the concentration thereof from exceeding about1.5 g/l.

15. A process according to claim 12 wherein the amount of saidsurfactant is at least about 0.05 g/l.

16. A process according to claim 15 wherein the amount of saidsurfactant is about 0.1 to about 0.5 g/l.

17. A process according to claim 16 wherein said surfactant is anatmospheric surfactant.

18. A process according to claim 15 wherein said surfactant is anamphoteric surfactant.

19. A process according toclaim 18 wherein said coating compositionincludes a black pigment.

20. A process according to claim 12 wherein said composition comprises:

a. styrene-butadiene copolymer resin solids; b. about l to about g/l ofhydrofluoric acid; and c. about 1.5 to about 6 g/l of hydrogen peroxideand wherein the pH of said composition is about 1.6 to about 3.0,wherein said metallic surface is a ferriferous surface, wherein saidmetal ions are iron ions and wherein iron ions are removed from thecomposition to keep the concentration thereof from exceeding about l.5g/l. 21. A process according to claim 20 wherein the amount of saidsurfactant is at least about 0.05 g/l.

22. A process according to claim 21 wherein the amount of saidsurfactant is about 0.1 to about 0.5 g/l.

23. A process according to claim 22 wherein said surfactant is anamphoteric surfactant.

24. A process according to claim 21 wherein said surfactant is anamphoteric surfactant.

25. A process according to claim 24 wherein said coating compositionincludes a black pigment.

26. A process according to claim 12 wherein said composition iscontacted with an amount of ion exchange material that is at least about65 percent above the amount theoretically needed to remove apredetermined amount of said metal ions.

27. A process according to claim 26 wherein said metal ions are ironions and wherein said surfactant is an amphoteric surfactant.

28. A process according to claim 27 wherein said ion exchange materialis a nucleated polystyrene sulfonic acid.

29. A process according to claim 20 wherein said composition iscontacted with an amount of ion exchange material that is at least about65 percent above the amount theoretically needed to remove apredetermined amount of said metal ions.

30. A process according to claim 29 wherein said surfactant is anamphoteric surfactant.

31. A process according to claim 30 wherein said ion exchange materialis a nucleated polystyrene sulfonic acid.

32. A process for applying an organic coating to objects having ametallic surface comprising:

A. immersing said object in an acidic aqueous coating compositioncontaining dispersed solid particles of an organic coating-formingmaterial for a period of time sufficient to form on said metallicsurface an organic coating, the thickness or amount of which increasesduring at least a portion of the time said surface is immersed in saidcomposition, wherein said composition dissolves from said surface metalions which tend to cause said composition to become unstable;

B. contacting said composition with an ion exchange material whichremoves metal ions from said coating composition thereby maintainingsaid composition stable, wherein said coating composition, after beingtreated with said ion exchange material,

tends to form coatings which are grainy or textured in appearance; andincluding C. contacting said composition with said ion exchange materialin the presence of an amphoteric or cationic surfactant, wherein theamount of said surfactant is an amount sufficient to form on saidsurface a smooth coating or a coating which has a reduced grainy ortextured appearance.

33. A process according to claim 32 wherein said particles are resinparticles.

34. A process according to claim 33 including regenerating said ionexchange material by contacting it with a regenerating material thatcontains a sequestering agent which sequesters metal ions which aredisplaced from said ion exchange material.

35. A process according to claim 34 wherein said particles are resinparticles, wherein said metal ions are iron ions and wherein saidsequestering agent is oxalic acid, citric acid or glycolic acid.

36. A process according to claim 35 wherein said sequestering agent isoxalic acid.

37. A process according to claim 33 wherein said surfactant is includedin said composition in an amount of at least about 0.05 g/l.

38. A process according to claim 33 wherein the amount of saidsurfactant is at least about 0.1 g/l.

39. A process according to claim 38 wherein the amount of saidsurfactant is about 0.2 to about 0.5 g/l.

40. A process according to claim 38 wherein said metal ions are ironions.

41. A process according to claim 40 wherein said surfactant is anamphoteric surfactant.

42. A process according to claim 41 wherein said surfactant is either vi7 CH2 NW A i r C17Ha1-C-NC:H4O CHzC O 0N8.

OH CHZC 0 ONE. (Formula I) C 2 IE1 (EH2 C11 23ON-C2H4 CHaC O ONa 0H CH2C0 0N3. (Formula II) 43. A process according to claim 40 wherein saidcomposition is contacted with an amount of ion exchange material that isat least about 65 percent above the amount theoretically needed toremove a predetermined amount of said iron ions.

44. A process according to claim 33 including regenerating said ionexchange material by contacting it with a regenerating acidic materialthat is an ingredient of said composition.

45. A process according to claim 44 wherein said particles are resinparticles, wherein said metal ions are iron ions, wherein saidcomposition contains phosphoric acid and wherein said ion exchangematerial is regenerated by contacting it with phosphoric acid.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3, 839097 Dated October 1, 1974 In en Wilbur S. Hall and Harrv M. Leister Itis certified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

IN THE SPECIFICATION Column 13, line 21, "occuring" should read-occurring-.

Column 17, line 45, "'mamterial" should read -material-.

' Column 18, lines 20 and 21, "centi-menter" should read -centimeter-.

Column 18, line 51, "varius" should read --various--.

Column 25, line 1', "utilizinng" should read -utilizing-.

I IN THE CLAIMS Claim 12, line 21, "compositions" should readcomposition--.

Claim 13, line 3, delete "of", second occurrence.

Claim 17, line 2, "atmospheric" should read amphoteric-.

Signer and sealed this 7th day of January T l-75.

4 7 isg amm H-M- r A Attest:

McCOY M, GIBSON JR. C. MARSFALL DANN attesting-Officer Cou issioner ofPatents FORM po'w5o (m'eg) I USCOMM-DC eoavema 1.5, GOVERNMENT PRINTINGOFFICE: 989 0-355-33

1. IN THE PROCESS FOR APPLYING AN ORGANIC COATING TO OBJECTS HAVING AMETALLIC SURFACE BY IMMERSING SAID OBJECT IN AN ACIDIC AQUEOUS COATINGCOMPOSITION CONTAINING DISPERSED SOLID PARTICLES OF AN ORGANICCOATING-FORMING MATERIALSURFACE AN ORGANIC COATING, THE FORM ON SAIDMETALLIC SURFACE AN ORGANIC COATING, THE THICKNESS OR AMOUNT OF WHICHINCREASES DURING AT LEAST A PORTION OF THE TIME SAID SURFACE IS IMMERSEDIN SAID COMPOSITIO, WHEREIN SAID COMPOSITION DISSOLVES FROM SAID SURFACEMETAL IONS WHICH TEND TO CAUSE SAID COMPOSITION ; AND WHEREIN SAIDPARTICLES HAVE A SIZE WITHIN THE RANGE OF ABOUT 0.01 TO ABOUT 0.1 MICRONAND LARGER; AND WHEREIN SAID COMPOSITION IS CONTACTED WITH AN IONEXCHANGE MATERIAL WHICH REMOVES SAID METAL IONS FROM SAID COATINGCOMPOSITION THEREBY MAINTAINING SAID COMPOSITION STABLE; AND WHEREINSAID COATING COMPOSITION PRIOR TO BEING CONTACTED WITH SAID ION EXCHANGEMATERIAL FORMS ON SAID SURFACE A SMOOTH OR GLOSSY COATING; AND WHEREINSAID COMPOSITION AFTER BEING TRETED WITH SAID ION EXCHANGE MATERIALTENDS TO FORM A SAID SURFACE A COATING WHICH IS GRAINY OR TEXTURE INAOPERARANCE; THE IMPROVEMENT COMPRISING CONTACTING SAID COMPOSITION WITHSAID ION EXCHANGE MATERIAL IN THE PRESENCE OF A DISPERSING AGENT WHICHIS EFFECTIVE IN MAINTAINING DISPERSED IN SAID COMPOSITION SAID PARTICLESHAVING A SIZE WITHIN THE RANGE OF ABOUT 0.01 TO ABOUT 0.1 MICRON, ANDTHEREAFTER COATING SAID METALLIC SURFACE WITH THE THUS TREATEDCOMPOSITION CONTAINING SAID PARTICLES HAVING A SIZE WITHIN THE RANGE OFABOUT 0.01 TO ABOUT 0.1 MICRON THEREBY FORMING ON SAID METALLIC SURFACEA SMOOTH COATING OR COATING WHICH HAS A REDUCED GRAINY OR TEXTUREAPPEARANCE.
 2. A process according to claim 1 wherein said particles areresin particles.
 3. A process according to claim 2 wherein saiddispersing agent is a protective colloid.
 4. A process according toclaim 2 wherein said coating composition includes a black pigment.
 5. Aprocess according to claim 2 wherein said dispersing agent is asurfactant having cationic properties in said acidic aqueouscomposition.
 6. A process according to claim 5 wherein said surfactantis an amphoteric surfactant.
 7. A process according to claim 6 whereinthe amount of said amphoteric surfactant in said composition is at leastabout 0.05 g/l.
 8. A process according to claim 7 wherein the amount ofsaid amphoteric surfactant in said composition is about 0.1 to about 0.5g/l.
 9. A process according to claim 5 wherein said composition iscontacted with an amount of ion exchange material that is at least about65 percent above the amount theoretically needed to remove apredetermined amount of said metal ions.
 10. A process according toclaim 9 wherein said metal ions are iron ions and wherein saidsurfactant is an amphoteric surfactant.
 11. A process according to claim10 wherein said ion exchange material is a nucleated polystyrenesulfoniC acid.
 12. A process for applying a coating to objects having ametallic surface comprising: A. immersing said object in an acidicaqueous coating composition which comprises: a. about 5 g/l to about 550g/l of resin dispersed in the composition, the source of the resin beinga latex thereof; b. about 0.4 g/l to about 5 g/l of fluoride ion; c. anoxidizing agent selected from the class consisting of H2O2 anddichromate, said agent being present in an amount sufficient to providefrom about 0.01 to about 0.2 of oxidizing equivalent per liter ofcomposition; and d. hydrogen ion in an amount sufficient to impart a pHto the composition of about 1.6 to about 3.8 wherein said compositiondissolves from said surface metal ions which tend to cause saidcomposition to become unstable; B. contacting said composition with anion exchange material which removes metal ions from said coatingcompositions thereby maintaining said composition stable, wherein saidcomposition after being contacted with said ion exchange material tendsto form on said metallic surface a coating which is grainy or texturedin appearance; and C. contacting said composition with said ion exchangematerial in the presence of an amphoteric or cationic surfactant in anamount sufficient to form on said surface a smooth coating or a coatingwhich has a reduced grainy or textured appearance.
 13. A processaccording to claim 12 wherein said metallic surface is a ferriferoussurface, wherein said metal ions are iron ions and wherein theconcentration of of iron ions in the composition is maintained belowabout 3 g/l.
 14. A process according to claim 13 wherein iron ions areremoved from the composition to keep the concentration thereof fromexceeding about 1.5 g/l.
 15. A process according to claim 12 wherein theamount of said surfactant is at least about 0.05 g/l.
 16. A processaccording to claim 15 wherein the amount of said surfactant is about 0.1to about 0.5 g/l.
 17. A process according to claim 16 wherein saidsurfactant is an atmospheric surfactant.
 18. A process according toclaim 15 wherein said surfactant is an amphoteric surfactant.
 19. Aprocess according to claim 18 wherein said coating composition includesa black pigment.
 20. A process according to claim 12 wherein saidcomposition comprises: a. styrene-butadiene copolymer resin solids; b.about 1 to about 5 g/l of hydrofluoric acid; and c. about 1.5 to about 6g/l of hydrogen peroxide and wherein the pH of said composition is about1.6 to about 3.0, wherein said metallic surface is a ferriferoussurface, wherein said metal ions are iron ions and wherein iron ions areremoved from the composition to keep the concentration thereof fromexceeding about 1.5 g/l.
 21. A process according to claim 20 wherein theamount of said surfactant is at least about 0.05 g/l.
 22. A processaccording to claim 21 wherein the amount of said surfactant is about 0.1to about 0.5 g/l.
 23. A process according to claim 22 wherein saidsurfactant is an amphoteric surfactant.
 24. A process according to claim21 wherein said surfactant is an amphoteric surfactant.
 25. A processaccording to claim 24 wherein said coating composition includes a blackpigment.
 26. A process according to claim 12 wherein said composition iscontacted with an amount of ion exchange material that is at least about65 percent above the amount theoretically needed to remove apredetermined amount of said metal ions.
 27. A process according toclaim 26 wherein said metal ions are iron ions and wherein saidsurfactant is an amphoteric surfactant.
 28. A process according to claim27 wherein said ion exchange material is a nucleated polystyrenesulfonic acid.
 29. A process according to claim 20 wherein saidcomposition is contacted With an amount of ion exchange material that isat least about 65 percent above the amount theoretically needed toremove a predetermined amount of said metal ions.
 30. A processaccording to claim 29 wherein said surfactant is an amphotericsurfactant.
 31. A process according to claim 30 wherein said ionexchange material is a nucleated polystyrene sulfonic acid.
 32. Aprocess for applying an organic coating to objects having a metallicsurface comprising: A. immersing said object in an acidic aqueouscoating composition containing dispersed solid particles of an organiccoating-forming material for a period of time sufficient to form on saidmetallic surface an organic coating, the thickness or amount of whichincreases during at least a portion of the time said surface is immersedin said composition, wherein said composition dissolves from saidsurface metal ions which tend to cause said composition to becomeunstable; B. contacting said composition with an ion exchange materialwhich removes metal ions from said coating composition therebymaintaining said composition stable, wherein said coating composition,after being treated with said ion exchange material, tends to formcoatings which are grainy or textured in appearance; and including C.contacting said composition with said ion exchange material in thepresence of an amphoteric or cationic surfactant, wherein the amount ofsaid surfactant is an amount sufficient to form on said surface a smoothcoating or a coating which has a reduced grainy or textured appearance.33. A process according to claim 32 wherein said particles are resinparticles.
 34. A process according to claim 33 including regeneratingsaid ion exchange material by contacting it with a regenerating materialthat contains a sequestering agent which sequesters metal ions which aredisplaced from said ion exchange material.
 35. A process according toclaim 34 wherein said particles are resin particles, wherein said metalions are iron ions and wherein said sequestering agent is oxalic acid,citric acid or glycolic acid.
 36. A process according to claim 35wherein said sequestering agent is oxalic acid.
 37. A process accordingto claim 33 wherein said surfactant is included in said composition inan amount of at least about 0.05 g/l.
 38. A process according to claim33 wherein the amount of said surfactant is at least about 0.1 g/l. 39.A process according to claim 38 wherein the amount of said surfactant isabout 0.2 to about 0.5 g/l.
 40. A process according to claim 38 whereinsaid metal ions are iron ions.
 41. A process according to claim 40wherein said surfactant is an amphoteric surfactant.
 42. A processaccording to claim 41 wherein said surfactant is either
 43. A processaccording to claim 40 wherein said composition is contacted with anamount of ion exchange material that is at least about 65 percent abovethe amount theoretically needed to remove a predetermined amount of saidiron ions.
 44. A process according to claim 33 including regeneratingsaid ion exchange material by contacting it with a regenerating acidicmaterial that is an ingredient of said composition.
 45. A processaccording to claim 44 wherein said particles are resin particles,wherein said metal ions are iron ions, wherein said composition containsphosphoric acid and wherein said ion exchange material is regenerated bycontacting it with phosphoric acid.